1. Field of the Invention
This invention relates to a device and method for separating heavier and lighter fractions of a fluid sample. More particularly, this invention relates to a device and method for collecting and transporting fluid samples whereby the device and fluid sample are subjected to centrifugation in order to cause separation of a heavier fraction from a lighter fraction of a fluid sample.
2. Description of Related Art
Diagnostic tests may require separation of a patient""s whole blood sample into components, such as serum or plasma, a lighter phase component, and red blood cells, a heavier phase component. Samples of whole blood are typically collected by venipuncture through a cannula or needle attached to a syringe or an evacuated collection tube. Separation of the blood into serum or plasma is then accomplished by rotation of the syringe or tube in a centrifuge. Such arrangements use a barrier for moving into an area adjacent the two phases of the sample being separated to maintain the components separated for subsequent examination of the individual components.
A variety of devices have been used in collection containers to divide the area between the heavier and lighter phases of a fluid sample. Many of these devices include mechanical barriers or partitions which are positioned within the lower collection tube. Upon centrifugation, the barrier becomes relocated within the tube between the separated blood phases.
Other separators include the use of thixotropic gel materials such as polyester gels in a tube. Such polyester gel serum tubes require special manufacturing equipment to prepare the gel and to fill the tubes. Moreover, the shelf-life of the product is limited in that, over time, globules may be released from the gel mass. These globules have a specific gravity that is less than the separated serum and may float in the serum and may clog certain measuring instruments, such as the instrument probes used during the clinical examination of the sample collected in the tube. Such clogging can lead to considerable downtime for the instrument to remove the clog.
No commercially available gel is completely chemically inert to all analytes. If certain drugs are present in the blood sample when it is taken, there can be an adverse chemical reaction with the gel interface.
Therefore, a need exists for a separator device that (i) is easily and inexpensively manufactured; (ii) is easily used to separate a blood sample; (iii) is independent of temperature during storage and shipping; (iv) is stable to radiation sterilization; (v) employs the benefits of a thixotropic gel barrier yet avoids the many disadvantages of placing a gel in contact with the separated blood components; (vi) minimizes cross contamination of the heavier and lighter phases of the sample during centrifugation; (vii) minimizes adhesion of the lower and higher density materials against separator device; (viii) is able to move into position to form a barrier in less time than conventional methods and devices; (ix) is able to provide a clearer specimen with less cell contamination than conventional methods and devices; and (x) can be used with standard sampling equipment.
The present invention provides a fluid separation device for maintaining separation of centrifuged fluids having first and second phases of respective densities. The device includes an elongate collection tube for accommodating fluids, and a deformable separator disposed within said tube. The separator is a ring-shaped bladder, having a configuration including a tubular passage for movement of the fluids therethrough. The bladder contains a flowable substance with a density intermediate the densities of the first and second phases of the fluids. The bladder furthermore is movable upon centrifugation to a position between separated first and second phases of the fluids, and is reconfigurable after centrifuge into a disk-like configuration along the tubular passage, establishing a separation between the first and second phases of the fluids.
The present invention also provides a method of separating and maintaining separation of fluids of first and second phases of respective densities. The method of separating collected blood fluids in heavy and light phases comprises the steps of first providing an elongate blood collection tube having a deformable separator resident therein. The deformable separator is generally toroidal in shape and contains a medium therein with a density such that the density of the bladder and medium combined is intermediate the respective densities of said heavy and light fluid phases. Collected blood fluids are placed in the tube and the tube is centrifuged to cause blood separation into said heavy and light phases. Centrifugation also causes the deformable separator to move in-between the phases and reconfigure from the generally toroidal shape having a passage therethrough for passage of fluids to a disk-like shape, which maintains separation between said separated phases of said fluids.
The device of the present invention is advantageous over existing separation devices in that it provides a more efficient separation of different phases of blood by the deformable bladder walking up the sides of the cylinder collection tube, while allowing flow of heavier fluids and cellular material through a central tubular passage of the separator.
A particular advantage of the device is that there is no shearing of the clot, as it is moving in the same direction as the inside of the toroidal-shaped tubular separator. The speed of the movement may be dictated by how quickly the clot separates and forms a density gradient, but can also be modified by the type of gel, or other substance used within bladder. For example, the lower the viscosity, the faster the movement of the separator, and hence the quicker the separation.
Furthermore, the deformable separator is advantageous to use, in that it has great tolerance variations due to its deformability. For example, it may be used with many different elongate collection tubes as it is highly tolerant to any variations between different tubes. Since it is essentially a deformable bladder, the separator adjusts easily to the collection tube, and is malleably positioned in both disk-like and toroidal configuration.